Generally, a magnetic-type position detector detects a change in the position of a detection object relative to a reference part. The magnetic-type position detector may utilize a magnetic flux generator such as a magnet. For example, a position detector disclosed in a patent document 1 (i.e., Japanese Patent Laid-Open No. JP-A-H08-292004) is configured to form a closed magnetic circuit having two magnets and two magnetic flux transmission parts that are disposed on a reference part. In such structure, the two magnets are respectively bound by the ends of the two mutually-facing magnetic flux transmission parts. A flow of spill magnetic fluxes from one transmission part to the other occurs within a gap between the respective ends of the two magnetic flux transmission parts. A magnetic flux density detector is configured to move together with the detection object within the gap between the two magnetic flux transmission parts and to output a detection signal according to the magnetic flux passing therethrough. In such manner, the position detector detects the position of the detection object relative to the reference part based on an output signal that is output from the magnetic flux detector.
In the position detector of a patent document 1, two magnets of the same magnet type having the same volume are disposed at both ends of each of the two magnetic flux transmission parts, with the polarity of the two magnets arranged in opposite directions to each other. Therefore, at the center of the gap between the two magnetic flux transmission parts, the direction of the magnetic flux is reversed. In other words, a center position of a movable range of the detection object and the magnetic flux density detector is a position where an absolute value of the magnetic flux density decreases to a minimum value (hereinafter “minimum MF density position”).
Generally, it is observed that the minimum magnetic flux density position within the movable range of the detector provides temperature-resistance against the effects of temperature changes due to the detector environment. That is, at such a position, the magnetic power of the magnets changes minimally even when the temperature of the detector environment changes (i.e., a temperature coefficient of the magnetic flux generator is low at such position). In other words, at the minimum magnetic flux density position, a position detection accuracy of the detector is higher than at other positions. Such a characteristic of the detector in the patent document 1 is perceived as having lower position detection accuracy at positions other than the center position of the detector movable range. That is, at both ends of the detector movable range (i.e., the gap), for example, the position detection accuracy of the detector may be low. Such a characteristic of the detector may also be interpreted as having a high position detection accuracy that occurs only at a center position of the detector movable range, which may be undesirable in some applications. That is, for example, when high position detection accuracy is required at both ends of the detector movable range, a position detector having low position detection accuracy at the ends of the detector movable range may not be suitable for certain applications.